From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinod Koul Subject: Re: [PATCH v4] dmaengine: omap-dma: add support for pause of non-cyclic transfers Date: Tue, 18 Oct 2016 20:22:23 +0530 Message-ID: <20161018145223.GA2467@localhost> References: <20161010120755.26153-1-vigneshr@ti.com> <20161014050047.28447-1-vigneshr@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20161014050047.28447-1-vigneshr@ti.com> Sender: linux-kernel-owner@vger.kernel.org To: Vignesh R Cc: Sebastian Andrzej Siewior , Peter Ujfalusi , Russell King - ARM Linux , linux-omap@vger.kernel.org, dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-omap@vger.kernel.org On Fri, Oct 14, 2016 at 10:30:47AM +0530, Vignesh R wrote: > From: Sebastian Andrzej Siewior > > This DMA driver is used by 8250-omap on DRA7-evm. There is one > requirement that is to pause a transfer. This is currently used on the RX > side. It is possible that the UART HW aborted the RX (UART's RX-timeout) > but the DMA controller starts the transfer shortly after. > Before we can manually purge the FIFO we need to pause the transfer, > check how many bytes it already received and terminate the transfer > without it making any progress. > > From testing on the TX side it seems that it is possible that we invoke > pause once the transfer has completed which is indicated by the missing > CCR_ENABLE bit but before the interrupt has been noticed. In that case the > interrupt will come even after disabling it. > > The AM572x manual says that we have to wait for the CCR_RD_ACTIVE & > CCR_WR_ACTIVE bits to be gone before programming it again here is the > drain loop. Also it looks like without the drain the TX-transfer makes > sometimes progress. > > One note: The pause + resume combo is broken because after resume the > the complete transfer will be programmed again. That means the already > transferred bytes (until the pause event) will be sent again. This is > currently not important for my UART user because it does only pause + > terminate. Applied, thanks -- ~Vinod